1. Field of the Invention
The present invention relates to catalyzed enantioselective amination and etherification reactions and catalysts, and more specifically to iridium-catalyzed enantioselective amination and etherification of allylic esters with primary or secondary amines, phenoxides, or alkoxides, as well as catalyst complexes comprising iridium and a phosphoramidite ligand.
2. Brief Description of the Related Art
Transition metal-catalyzed allylic substitution is a powerful tool for the controlled formation of carbon-carbon and carbon-heteroatom bonds (Godleski, S. A.; Trost, B. M., Fleming, I., Eds.; Pergamon Press: New York, 1991; Vol. 4, pp 585-661). Most enantioselective versions of these reactions with carbon nucleophiles have been reported with Pd (Jacobsen, E. N. et al., Comprehensive Asymmetric Catalysis I-III; Springer-Verlag: Berlin, Germany, 1999), but enantioselective allylic alkylation has also been reported with Mo (Trost, B. M.; Hachiya, I. J. Am. Chem. Soc. 1998, 120, 1104; Trost, B. M.; Hildbrand, S.; Dogra, K. J. Am. Chem. Soc. 1999, 121, 10416; Malkov, A. V.; Baxendale, I. R.; Dvorak, D.; Mansfield, D. J.; Kocovsky, P. joc 1999, 64, 2737), W (Lloyd-Jones, G. C.; Pfaltz, A. Angew. Chem., Int. Ed. 1995, 34, 462; Malkov, A. V.; Baxendale, I. R.; Dvorak, D.; Mansfield, D. J.; Kocovsky, P. joc 1999, 64, 2737), and, most recently, Ir catalysts (Takeuchi, R. Synlett 2002, 1954; Takeuchi, R.; Ue, N.; Tanabe, K.; Yamashita, K.; Shiga, N. J. Am. Chem. Soc. 2001, 123, 9525; Bartels, B.; Garcia-Yebra, C.; Rominger, F.; Helmchen, G. Eur. J. Inorg. Chem. 2002, 2569). However, despite the importance of optically active allylic amines and ethers, few enantioselective allylic aminations and etherifications by reactions of heteroatom nucleophiles have been described.
Enantioselective routes to optically active amines can provide valuable synthetic building blocks. The enantioselective preparation of chiral tertiary amines is particularly important because they cannot be generated directly by enantioselective hydrogenation of imines, and the enantioselective hydrogenation of enamines remains a challenge. In addition, methods for enantioselective coupling of two fragments by C—N bond-formation are limited.
Allylic substitution of acyclic allylic electrophiles catalyzed by W, Mo, Ru, Ir, and Rh complexes often generate the chiral branched substitution products. Enantioselective amination of symmetrical 1,3-diphenylallyl carbonates and unsymmetrical branched allylic acetates along with a few examples of palladium-catalyzed asymmetric amination of a terminal allylic ester or carbonate have been reported (Hayashi, T. et al., J. Am. Chem. Soc. 1989, 111, 6301-6311; You, S. et al., J. Am. Chem. Soc. 2001, 123, 7471; Hayashi, T. et al., Tetrahedron Lett. 1990, 31, 1743-1746; Johannsen, M.; Jørgensen, K. A. Chem. Rev. 1998, 98, 1689-1708). Takeuchi (Takeuchi, R.; et al., J. Am. Chem. Soc. 2001, 123, 9525-9534) and Evans (Evans, P. A.; et al., J. Am. Chem. Soc. 1999, 121, 6761-6762) have shown that iridium and rhodium complexes of achiral phosphites catalyze the formation of branched amines, in some cases with conservation of enantiomeric excess. Helmchen reported enantioselective alkylation of branched allylic acetates with modest levels of enantiomeric excess (ee) (Bartels, B.; Helmchen, G. Chem. Commun. 1999, 741-742) in the presence of an iridium-phosphoramidite catalyst. Analogous enantioselective aminations occurred with ee's below 15%. A general, enantioselective allylic amination from an achiral, terminal allylic electrophile has not been accomplished.
Aryl ethers are common subunits of biologically active molecules. Apart from their use as precursors for the Claisen rearrangement (Wipf, P.; Trost, B. M., Fleming, I., Paquette, L. A., Eds.; Pergamon press: Oxford, 1991; Vol. 5, pp 827-874; Larock, R. C. Comprehensive Organic Transformations: A Guide to Functional Group Preparations; VCH Publishers, Inc: New York, 1989), aryl allyl ethers have not been used extensively as building blocks for natural product synthesis because methods for their enantioselective construction are limited. Two reports of stereospecific allylic etherification of branched carbonates catalyzed by Ru (Trost, B. M.; Fraisse, P. L.; Ball, Z. T. Angew. Chem., Int. Ed. 2002, 41, 1059) and Rh (Evans, P. A.; Leahy, D. K. J. Am. Chem. Soc. 2000, 122, 5012; Evans, P. A.; Leahy, D. K. J. Am. Chem. Soc. 2002, 124, 7882) were reported recently, and a few enantioselective palladium-catalyzed examples have been reported (Trost, B. M.; Toste, F. D. J. Am. Chem. Soc. 1995, 121, 4545; Trost, B. M.; Toste, F. D. J. Am. Chem. Soc. 1998, 120, 815; Trost, B. M.; Tsui, H.-C.; Toste, F. D. J. Am. Chem. Soc. 2000, 122, 3534). Elegant applications of the palladium-catalyzed chemistry for the synthesis of natural products demonstrates the potential of these building blocks in organic synthesis (Trost, B. M.; Toste, F. D. J. Am. Chem. Soc. 1998, 120, 9074; Trost, B. M.; Toste, F. D. J. Am. Chem. Soc. 2000, 122, 11262; Trost, B. M.; Thiel, O. R.; Tsui, H.-C. J. Am. Chem. Soc. 2002, 124, 11616; Trost, B. M.; Tang, W. J. Am. Chem. Soc. 2002, 124, 14542) Thus, new, more general, enantioselective methods for the construction of allylic ethers would be synthetically valuable.
International Patent Publication WO 02/04466 discloses catalysts for asymmetric transfer hydrogenation, including a transition metal selected from rhodium and ruthenium, and a phosphoramidite ligand. This publication also discloses processes for the asymmetric transfer hydrogenation of an olefinically unsaturated compound, ketone, imine or oxime derivative in the presence of a hydrogen donor and a catalyst, wherein the catalyst includes a transition metal selected from rhodium, ruthenium, and iridium, and a ligand.
International Patent Publication WO 01/23088 discloses catalysts for asymmetric transfer hydrogenation using a transition metal catalyst and a nitrogen-containing enantiomerically enriched ligand, as well as processes for the preparation of enantiomerically enriched compounds using such catalysts. According to the invention, the transition metal is iridium, ruthenium, rhodium or cobalt, and the enantiomerically enriched ligand contains sulfur in the form of a thioether or a sulfoxide.
Bartels et al., (Bartels, B.; Garcia-Yebra, C.; Rominger, F.; Helmchen, G. Eur. J. Inorg. Chem. 2002, 2569-2586) discloses Ir-catalysed allylic alkylations of enantiomerically enriched monosubstituted allylic acetates using P(OPh)3 as ligand. Lithium N-tosylbenzylamide was identified as a suitable nucleophile for allylic aminations.
What is needed in the art are catalysts and processes for enantioselective and regioselective reactions of terminal allylic electrophiles with compounds containing N—H or O—H bonds such as aliphatic amines, benzylamines, aromatic amines, phenoxides, or alkoxides, to produce optically active, branched allylic ethers or amines. The present invention is believed to be an answer to that need.